Integrating interacting drugs and genetic variations to improve the predictability of warfarin maintenance dose in Chinese patients

OBJECTIVE: Compared with genetic factors, drug interactions are largely unexplored in pharmacogenetic studies. This study sought to systematically investigate the effects of VKORC1, STX4A, CYP2C9, CYP4F2, CYP3A4, and GGCX gene polymorphisms and interacting drugs on warfarin maintenance dose. METHODS: A retrospective study of 845 Chinese patients after heart valve replacement receiving long-term warfarin maintenance therapy was conducted. Thirteen polymorphisms in the six genes were genotyped, and 36 drugs that may interact with warfarin were investigated. RESULTS: Single-nucleotide polymorphism association analysis showed that VKORC1, CYP2C9 and CYP4F2 variations were highly associated with the warfarin maintenance dose. Among 36 drugs that may interact with warfarin, fluconazole, amiodarone, and omeprazole were associated with the requirement for 45.8, 16.7, and 16.7% lower median warfarin dose (all P<0.05 with a false discovery rate <0.05). The final pharmacogenetic equation explained 43.65% of interindividual variation of warfarin maintenance dose with age, body surface area, VKORC1 g.3588G>A, CYP2C9*3, CYP4F2 c.1297G>A, amiodarone, fluconazole, and diltiazem accounting for 1.97, 2.74, 24.12, 3.94, 1.64, 5.92, 2.47, and 0.84% of variation. CONCLUSION: The present study indicated that VKORC1, CYP4F2, and CYP2C9 genotypes and interacting drugs had a significant impact on the warfarin maintenance dose in Chinese patients with heart valve replacement and demonstrated that integrating interacting drugs can largely improve the predictability of the dose algorithm.